Thermoformable laminate structure

ABSTRACT

A moisture resistant, moldable, thermoformable laminate structure comprising a layer of foamed thermoplastic material having a polymer-impregnated cloth bonded to one surface thereof.

This application is a continuation in part of applications Ser. Nos.553,594 and 553,462, both filed Nov. 21, 1983 and incorporated herein byreference, now U.S. Pat. Nos. 4,476,183 and 4,489,126 respectively.

This invention relates to thermoplastic materials, and particularly to athermoformable laminate structure comprising foamed thermoplastic sheetwhich may be molded into complex shapes. More particularly thisinvention relates to a thermoformable laminate structure having acoating formed from a fabric which is impregnated with a polymer whichhas a high softening temperature.

BACKGROUND OF THE INVENTION

Foamed thermoplastic laminates have been used for many years. Theselaminates were most often formed as a sandwich structure in which thefoamed thermoplastic material was enclosed between liner board facings.An example of this construction is a polystyrene foam sheet which has akraft liner board facing on each side. This laminate has been used bydie-cutting and scoring or by pressing the board and applying a resin tofix the pressed shape. However, the kraft liner board facing is a papermaterial which is not easily molded and which has a tendency to wrinkleduring any molding of the laminate structure.

Other efforts have been made to provide a laminate structure which maymore easily be molded. A thermoplastic laminate has been formed of alayer of foamed styrene-maleic anhydride polymer to which athermoplastic polymer skin is bonded. This laminate is moldable withoutthe problems caused by the earlier developed paper facings.

More recent efforts have provided laminate structures formed of moldedfiberglass which contains a phenol-formaldehyde polymer as a binder. Arayon scrim is attached to one side of a fiberglass batt and iscompression molded to the desired shape

SUMMARY OF THE INVENTION

It is an object of this invention to provide a moldable thermoformablelaminate structure.

It is a further object of this invention to provide amoisture-resistant, moldable, thermoformable laminate structure formedfrom a foamed thermoplastic sheet which has a polymer impregnated fabricon one face.

It is yet another object of this invention to provide amoisture-resistant, moldable, thermoformable laminate structure formedfrom a layer of foamed thermoplastic material which is faced by a fabricimpregnated with an acrylic polymer having a high softening temperature.

An additional object of this invention is to provide a method forfabricating the moisture-resistant, moldable, thermoformable laminatestructure.

These and other objects are obtained by the thermoformable laminatestructure of this invention and the method of fabrication describedhereinafter.

This invention provides a thermoformable laminate comprising a foamedthermoplastic sheet having adhered to one side a polymer-impregnatedcloth. Desirably the cloth comprises synthetic fibers and readilyelongates in any direction in its surface. The cloth is impregnated witha polymer has a softening temperature greater than 75° C.

Such thermoformable laminates are useful in providing molded laminatesheets by thermoforming methods. The thermoformable laminates of thisinvention are particularly useful in providing composite laminatestructures which are moldable into complex shapes, for example for useas an automobile headliner, which is the covering for the interiorsurface of an automobile roof. Such composite laminate may utilize thethermoformable laminate of this invention in conjunction with otherlayers to provide a composite laminate with enhanced sound-adsorbingqualities. Such composite laminates are disclosed in copendingapplication Ser. No. 553,594, filed Nov. 21, 1983, U.S. Pat. No.4,476,183 incorporated herein by reference.

DESCRIPTION OF PREFERRED EMBODIMENTS

The thermoformable laminate of this invention comprising a foamedthermoplastic sheet having adhered to one side a polymer-impregnatedcloth is preferably fabricated utilizing a polymer having a softeningtemperature of at least 75° C.

The foamed thermoplastic sheet can comprise a variety of foamablethermoplastic materials for instance polystyrene, styrene copolymerssuch as styrene-maleic anhydride polymer and styrene-acrylonitrilepolymer, and the like. Foamed thermoplastic material may also compriseother foamable thermoplastic material which would be substantially rigidat moderate temperatures for instance polyolefins such as polyethylene.However, adhesion to polyethylene is generally difficult without surfacetreatment such as flame treating. The preferred material for providingthe foamed thermoplastic sheet useful in a laminate of this inventioncomprises polystyrene or copolymers of polystyrene which arethermoformable at temperatures up to about 180° C.

The foamed thermoplastic sheet can be provided in any thickness desired.Foamed thermoplastic sheet which is particularly useful in the laminateof this invention will generally be less than 30 millimeters inthickness. The preferred thickness of the foamed thermoplastic sheet foruse in fabricating composite laminates will generally be between 2millimeters and 20 millimeters.

The thermoformable laminate of this invention has a polymer-impregnatedcloth adhered to one side of the foamed thermoplastic sheet. Thepolymer-impregnated cloth provides stability to the laminate, forinstance a composite laminate, which has been thermoformed into acomplex shape.

Thermoforming of such laminates can be accomplished by preheating thelaminate to a temperature at which the foamed thermoplastic materialreadily thermoforms without foam collapse. It is generally convenient tomeasure surface temperature of the preheated laminate prior tothermoforming. When styrenic foamed material is used, the surfacetemperature of the laminate should generally be above 120° C., belowwhich the laminate may be thermoformable but susceptible to cracking orsurface wrinkling. When styrenic foamed material is used, the surfacetemperature should be low enough to avoid foam collapse, for instanceabout 150° C. for polystyrene foam and 180° C. for styrene-maleicanhydride copolymer foam.

For purposes of this invention the term "softening temperature" isintended to mean softening point as determined by thermomechanicalanalysis using a program designated "TADS TMS Std TEV01.04 PCN05.06B01.01.04" provided by Perkin Elmer using a Perkin Elmer: ModelTMS2, Thermomechanical Analyzer. Analytical parameters were: probe load:10 grams; minimum temperature: 25° C.; maximum temperature: 200° C.;heating rate: 5° C. per minute; cooling rate: 20° C. per minute;penetration probe: round tip. Polymer samples were approximately 1/4inch×1/8 inch×1/16 inch (6.35 mm×3.18 mm×1.6 mm). Thermomechanicalanalysis comprises placing a weighted compression probe on a thin samplewhich is slowly heated at a uniform rate. The temperature at which theprobe begins to penetrate the sample is the softening point which isdetermined by the intersection of tangent lines about the inflectionpoint on the plot of penetration distance versus temperature near thetemperature at which the probe begins to penetrate the sample. Polymersuseful in the process of this invention will have a softeningtemperature greater than 75° C. but lower than the minimum thermoformingmaterial, for instance about 130° C. or up to about 180° C.

The cloth can comprise a variety of textile structures for instance thecloth may be woven or non-woven. A desired characteristic of the clothis that it elongates sufficiently in a direction in its surface toconform to the desired complex shape to be imparted by the thermoformingprocess. Desirable cloth will comprise a fabric that can elongate, forinstance in the range of about 10-50 percent, at thermoformingtemperature without destroying integrity of the fabric structure. Wovencloths of natural or glass fibers generally exhibit elongation of lessthan 10 percent. Preferred cloth which can undergo such elongationcomprises non-woven fabric such as non-woven spunbonded polyesterfabric. Other cloths which may be useful include non-woven polyester,non-woven nylon and non-woven polypropylene. The cloth can have anythickness which may be desired. Typically useful cloth will have athickness in the range of 0.05 to 1.0 millimeters. However, cloth havinga larger thickness may be used. Preferably cloth will be non-woven andhave a thickness of foam 0.1 to 0.4 millimeters. Typecally useful clothwill also have a basis weight in the range of 0.3 to 10.0 ounces persquare yard (10-340 grams per square meter), preferably in the range of1.0 to 6.0 ounces per square yard (34-203 grams per square meter).

The polymer-impregnated cloth can be prepared by soaking the cloth in asolution of polymer and solvent, for instance cloth can be pulledthrough a vat of a solution and then through a set of rolls to removeexcess solution. The cloth can be dried to remove excess solvent andthen adhered to one side of the foamed thermoplastic sheet. The adhesioncan be effected by any adhesive that will bond the polymer-impregnatedcloth to the foamed thermoplastic sheet. Preferably the adhesive willnot exhibit creep at low temperatures for instance below the softeningtemperature of the foam. Acrylic adhesives are useful for this purpose.

Desirable soluble polymers include those polymers which are designatedin commerce as resins. Polymers that are soluble in liquids such aswater and lower alcohols such as methanol, ethanol, N-propanol, etc. arepreferred. The most preferred polymers are those which are soluble inwater, for instance solutions of water and ammonia. Such resins includeacrylic resins, such as styrene-methacrylic acid copolymers. One suchacrylic resin which is soluble in a water-ammonia solution is availablefrom S. C. Johnson & Son, Inc as Joncryl 678 acrylic resin, which has asoftening temperature of 89° C.

Other resins such as a phenolic resin may also be used. When a phenolicresin is used instead of the preferred acrylic resin the fabricationprocess must be modified to prevent a complete cure of the phenolicresin before the laminate structure is molded into the desired finalshape. When the phenolic resin is completely cured it is no longermoldable; thus, during the preparation of the laminate structure, thephenolic resin impregnated fabric must be only partially cured. It mustremain partially cured until the final molding step. The use of anacrylic resin, which is preferred, eliminates the handling problems suchas storage to prevent curing and emission of volatile materials whichare associated with the use of a phenolic resin. The coating is bondedto one of the surfaces of the layer of foamed thermoplastic material.This may be accomplished by heat treatment during the laminating or byan adhesive which is preferably water dispersed.

Such acrylic resins must also of course exhibit a softening temperaturegreater than about 75° C. Such high softening temperature allows for astable laminate especially for uses where local temperatures may becomemoderately high.

Alternatively the thermoformable laminate of this invention can beprepared by applying a polymer emulsion film to the foamed thermoplasticsheet. A cloth can then be adhered to the wet polymer emulsion film.

This polymer emulsion film method is generally more economical in thatsubstantially lower quantities of polymer are required to form alaminate. For instance, it has been found that less than 16 grams (forinstance, about 5 to 8 grams) of polymer is required per square meter oflaminate by this alternative polymer emulsion film method. On the otherhand it has been generally found that about 40.0 grams of polymer areutilized per square foot of laminate when the cloth is soaked in apolymer solution. The cloth can be laid over the polymer emulsion film.The composite of cloth, polymer emulsion film and foamed thermoplasticsheet can then be calendered to force the polymer emulsion film topenetrate the cloth. The laminate can be formed by allowing the solventto evaporate from the polymer emulsion at the outer surface of thecloth.

Alternatively the polymer emulsion film overlaying a surface of thefoamed thermoplastic sheet can be allowed to dry prior to application ofthe cloth. The cloth can be applied to the dry film and the laminateformed by the application of heat and pressure. For instance a hotsurface having a temperature of about 120° to 150° C. can be pressed onthe cloth to cause the polymer film to penetrate into and impregnate thecloth.

A suitable polymer emulsion may contain an adhesive to promote adhesionof the polymer emulsion film to the foamed thermoplastic sheet. Suchadhesive can comprise an acrylic adhesive such as is available from Rohnand Haas as E2138 acrylic adhesive or E1958 acrylic adhesive. Suchadhesive can be mixed, for instance, in equal volumetric proportions,with the acrylic emulsion, such is available from S. C. Johnson & Son,Inc. as Joncryl 89 styrenated acrylic dispersion, a water based emulsionof about 48 percent by weight acrylic solids having a softeningtemperature of 101° C. The following structures illustrate laminatestructures made in accordance with this invention.

EXAMPLE I

This example ilustrates a method of forming the laminate structure ofthis invention.

A mixture of polymer emulsion was prepared by combining equal weights oftwo aqueous acrylic emulsions.

The first aqueous acrylic emulsion was identified as Joncryl™ 89styrenated acrylic dispersion (available from S. C. Johnson & Son, Inc.,Johnson Wax Chemical Products Division) which comprises 48±1 percent byweight solids in water at a pH in the range of 8.0 to 8.5. The emulsionhas a milky appearance, a viscosity in the range of 400 to 600centipoises and a density of 8.7 pounds per gallon (1.04 g/cm³).

The second aqueous acrylic emulsion was identified as adhesive E-2138(available from Rohm and Haas Company) which comprises 51 to 53 percentby weight acrylic polymer in water at a pH in the range of 8.2 to 8.6.The emulsion has a milky-blue color, a mild ammoniacal odor due to about25 ppm of ammonia, and contains about 0.5 ppm of formaldehyde. Theemulsion has a viscosity in the range of 40,000 to 50,000 centipoises.

The mixture of the two acrylic polymer emulsions was applied in a thinfilm to one surface of a sheet of polystyrene foam having a thickness ofabout 130 mils (3.3 mm) and a density of about 42 pounds per thousandsquare feet (205 grams per square meter). The film was applied at athickness of about 0.75 mil (19×10⁻⁶ m) with a No. 8 stainless steelmetering rod comprising No. 8 wire (having a diameter of 0.162 inches(4.1 mm)) wound on a rod having a diameter of 1/2 inch (about 13 mm).The emulsion film was applied at about 1.5 pounds per thousand squarefeet (7 gm/m²).

While the film was still wet, a piece of spun-bonded, non-wovenpolyester fabric was laid onto the emulsion coated surface of thepolystyrene foam. The polyester fabric had a basis weight of 1.0 ouncesper square yard (33.9 gm/m²) and is identified as Reemay 2014 by duPont.

The fabric was then laminated to the polystyrene foam in a WabashHydraulic Press, Model 50-2424-2 STMA, by which Metal Products, Inc.,having steam heated plates set for a temperature of 260° F. (127° C.).The press was equipped with shims which provided a forming cavity inwhich the foam was allowed to expand. The wet laminate was heated withinthe press for 30 seconds, after which the press was cooled for about 90seconds to a temperature of about 100° F. (38° C.). The laminate sheetthen had a thickness of about 150 mils (3.8 mm).

The polyester fabric was laminated to the polystyrene foam with goodadhesion. Adhesion can be determined by pulling the fabric to effectdelamination. If fibers from the non-woven fabric separate from thefabric and are left adhered to the foam, adhesion is consideredexcellent. If there is delamination with no fibers left on the foam,adhesion is considered good.

EXAMPLES II-V

The lamination procedure of Example I was repeated using a variety ofnon-woven fabrics.

II. Fabric: non-woven polypropylene having a basis weight of 68 gm/m².

Adhesion: good.

III. Fabric: non-woven polypropylene having a basis weight of 105 gm/m².

Adhesion: good.

IV. Fabric: non-woven polyester having a basis weight of 163 gm/m².

Adhesion: excellent.

V. Fabric: non-woven polyester having a basis weight of 197 gm/m².

Adhesion: excellent.

Although adhesion was only good in the laminates of Examples II and III,such laminates would be acceptable and suitable for less severeapplications.

EXAMPLE VI

This example illustrates the thermoformability of the laminate structureof this invention as prepared in Example 1.

The laminate structure prepared in Example 1 was thermoformed in a Cometthermoformer, Labmaster Model 14×20, by Comet Industries, Inc. Thethree-dimensional mold was of a design representing a seat buckle coveras used in some General Motors automobiles. The thermoformer operates bycarrying the flat laminate sheet into an infrared heater section topreheat the flat laminate sheet to a thermoforming temperature for thematerial of the sheet so that the sheet can be readily formed. The sheetwas in the heater section for 8 seconds where it reached a surfacetemperature in the range of 260° to 290° F. (127°-143° C.). The heatedsheet was then moved into the open mold block which was heated to 70° F.(21° C.). The cooled molded laminate had good three-dimensionaldefinition with no signs of delamination and no wrinkles.

EXAMPLES VII-X

The thermoforming procedure of Example VI was repeated using thelaminate structures prepared in Examples II-V.

VII. Thermoforming of the laminate sheet prepared in Example II. Thecooled molded laminate had good three-dimensional definition, but thepolypropylene fabric partially delaminated from the polystyrene foam.

VIII. Thermoforming of the laminate sheet prepared in Example III. Thecooled molded laminate had good three-dimensional definition, but thepolypropylene fabric partially delaminated from the polystyrene foam.

IX. Thermoforming of the laminate sheet prepared in Example IV. Thecooled molded laminate had good three-dimensional definition with nosigns of delamination and no wrinkles.

X. Thermoforming of the laminate sheet prepared in Example V. The cooledmolded laminate had good three-dimensional definition with no signs ofdelamination and no wrinkles.

Although there was some delamination and wrinkles in the laminatesthermoformed in Examples VII and VIII, such laminates comprisingpolypropylene fabric would be suitable for applications requiring lesssevere thermoforming, for instance, such as automobile headliners wherethe thermoforming mold would not draw as deeply or at sharp angles.

EXAMPLE XI

This example illustrates an alternative method of producing thethermoformable laminate structure of this invention.

A bath of acrylic polymer solution was prepared using Joncryl™ 61LVacrylic resin solution (available from S. C. Johnson & Son, Inc.) whichhas the following formulation:

acrylic resin--35.0 weight percent

28% aqueous ammonia--7.5 weight percent

ethylene glycol--1.5 weight percent

isopropyl alcohol--5.0 weight percent

water--51.0 weight percent

The acrylic resin component had a softening temperature of 85° C.

The acrylic polymer solution was diluted with water to an acrylic resinlevel of 27 percent by weight.

A sheet of spunbonded non-woven polyester fabric was soaked in the bathto impregnate the fabric with the acrylic polymer solution. Excesssolution was removed by passing the fabric through a pair ofrubber-coated squeeze rolls. The fabric was then placed in an oven at180° F. (82° C.) for five minutes to remove liquids providing a driedpolymer impregnated fabric, which comprised about 50 percent by weightacrylic polymer.

A sheet of polystyrene foam having a thickness of about 130 mils (3.3mm) and a density of about 42 pounds per thousand square feet (205 gramsper square meter) was coated on one surface with an aqueous acrylicemulsion identified as adhesive E-1958 (available from Rohm and HaasCompany) which comprises 57 to 59 percent by weight acrylic polymer inwater at a pH in the range of 4.0 to 5.0. The emulsion has a milky-whitecolor, a mild acrylic odor. The emulsion has a Brookfield viscosity inthe range of 2,000 to 4,000 centipoises. A catalyst solution of 15percent by weight of sesquicarbonate (equimolar amounts of sodiumbicarbonate and sodium carbonate) was added to the emulsion at a levelof 4 parts per 100 parts of the emulsion. The catalyzed emulsion wasapplied to the surface of the polystyrene foam with a No. 8 stainlesssteel metering rod comprising No. 8 wire (having a diameter of 0.162inches (4.1 mm)) wound on a rod having a diameter of 1.2 inch (13 mm)and allowed to dry.

The dried polymer impregnated fabric was applied to the surface ofpolystyrene foam coated with dried acrylic emulsion. Lamination waseffected in a Wabash Hydraulic Press, Model 50-2424-2 STMA, by MetalProducts, Inc. The press had steam heated plates at a temperature of260° F. (127° C.) which were spaced apart by shims to provide a formingcavity in which the polystyrene foam was allowed to expand. The laminatewas heated within the press for 30 seconds, after which the press wascooled for about 90 seconds to a temperature of about 100° F. (38° C.).The dry laminate structure then had a thickness of about 150 mils (3.8mm).

EXAMPLE XII

The thermoforming procedure of Example VI repeated using the laminatestructure prepared in Example XI. The cooled molded laminate had goodthree-dimensional definition with no wrinkles.

USES OF THE THERMOFORMABLE LAMINATE

The thermoformable laminate sheet of this invention is useful inpreparing molded thermoplastic foam articles.

Such molded thermoplastic foam articles are particularly useful whenthermal or sound insulation is a desired property. The laminate providesthree-dimensional rigidity over a wide temperature range.

This thermoformable laminate sheet is particularly useful in preparingheadliners for automobiles where the laminate provides for noiseattenuation within the automobile. A particular useful headliner can beprepared by utilizing two laminate sheets prepared according to thisinvention as covers for an inner core of a third polymeric foam, forinstance a 250 mil (6.35 mm) thick, soft polyether, polyurethane foam.The three part composite can be prepared by using an adhesive on thebare surface of the laminate sheet to adhere to the soft, foam core. Thecomposite has the acrylic emulsion adhered fabric on its outer surfaceswhich allows for thermoformability of the composite. One surface of thecomposite can be covered with a vinyl covered, soft foam trim for anaesthetic interior surface. Such automotive headliners are described incopending application Ser. No. 553,594.

While specific embodiments of the invention have been described, itshould be apparent to those skilled in the art that variousmodifications thereof can be made without departing from the true spiritand scope of the invention. Accordingly, it is intended that the scopeof the following claims cover all such modifications which fall withinthe full inventive concept.

We claim:
 1. A moisture-resistant, moldable, thermoformable laminatestructure comprising:(a) a layer of a substantially rigid foamedthermoplastic material, selected from the group consisting ofpolystyrene, styrene copolymers and polyethylene, said layer havingfirst and second surfaces; and (b) a coating bonded to one of saidsurfaces; said coating being a polymer-impregnated cloth; wherein saidpolymer is a styrene-methacrylic acid copolymer having a softeningtemperature greater than approximately 75° C.
 2. The laminate structureof claim 1 wherein the foamed thermoplastic material is selected fromthe group consisting of polystyrene, styrene-maleic anhydride polymerand styrene-acrylonitrile polymer.
 3. The laminate structure of claim 2wherein the layer of foamed thermoplastic material is a foamedpolystyrene.
 4. The laminate structure of claim 1 wherein said fabric isa woven cloth fabric.
 5. The laminate structure of claim 1 wherein saidcloth is a non-woven fabric.
 6. The laminate structure of claim 5wherein said non-woven cloth is a non-woven, spunbonded fabric.